Electrically heated catalysts (EHCs) have been developed over the last few years for controlling cold-start automobile exhaust emissions. Many technical obstacles will have to be overcome to commercialize EHCs. In particular, automobile designers will face system-related issues, due to the high power demands of the EHC. This paper is the result of an effort to acquire data that will help resolve those system-related issues.A fleet of 20 cars in normal driving service was equipped with operating EHC systems. This paper presents preliminary findings obtained after approximately six months of operation of the fleet. Preliminary battery and component durability are presented, as well as representative emission results.A second paper (Part II) is envisioned to present findings after approximately two years of operation.